Q: kernel panic when downgrading OS

if you are going to reinstall a previous version of the OS you really need to use the following article:

http://support.apple.com/kb/HT2597

hopefully this resolves the issues you're having. good luck

yes you can't buy snow leopard from the apple store directly but it's available at the apple online store for 19.99. you just have to search the store to find it. once you have the disks boot to those and erase the HD then reintall the snow leopard fresh.

however, if the backup you have was done w/ mt lion there may still be issues since you are going backward on the OS. may have to manually move info back to the mac after the clean install to get around those issues.

The 10.6 Snow Leopard DVD is in the Apple online store. You can get it for $19.99. http://store.apple.com/us/product/MC573/mac-os-x-106-snow-leopard